I made a hole that was two deep x 3 across x 2 across and filled it with water. The bottom was dirt and I changed half of the dirt to sand. I put one Sea Grass on each block. Everything was fine until I placed the final Sea Grass, at which point the water vanished. The water is still there, I can still float and it takes longer to fall, but it is invisible. Adding more water causes the sound effect, but does nothing. If I take one of the Sea Grasses away the water comes back, but it will disappear if I put it back.